They expect a permanent decline to begin soon due to trade, economy, and environment concerns.

Analysts believe that 2018 will go down as the best year for internal combustion vehicle sales ever, predicting a downturn in demand for the mode of propulsion starting in 2019.

"At the beginning of the year we had a more optimistic perspective for the global market," said Felipe Munoz, global automotive analyst for Jato Dynamics, in Financial Times. "This has changed in the last six months."

Predictions as of January were that internal combustion vehicle demand would continue to grow through 2022, but a plateau of sales in the three biggest vehicle markets of China, Europe, and the United States has meant that 2018 growth won't be as large as expected, and future years may see demand shrink instead.

"We will probably see the peak of combustion engine car sales in 2018 based on global sales through October, plus estimates for November and December," commented Munoz.

"When you look at 2018 since the summer, new car sales in all of the important markets are going down," added Axel Schmidt, global automotive lead for Accenture, in FT's story. "Selling combustion engine cars to customers—this will not grow in the future."

Attributed for the decrease in demand are factors such as the U.S.-China trade war, more restrictive emissions guidelines in Europe, and Brexit, among others. Slumping real income of the average American could also contribute to reduced sales of ICE vehicles in North America, though global vehicle sales aren't expected to decline. Moody's projects that electric vehicles' market share could quadruple to 1.6 percent, preventing the new car market from deflating.

This will in part be driven by the greater availability of affordable electric vehicles, especially those attractive to consumers, such as crossovers. Hyundai and Kia, in particular, will debut smaller, more affordable electric crossovers, but their range and livability don't suffer at the hands of reduced costs. One country that may gobble up these models is China, which is buying EVs in greater volumes than any other market. Fuel cell vehicles are increasing in popularity as well, though automakers are split on whether or not hydrogen fuel cells are tomorrow's means of propulsion.